For the past 14 years, the invasive species known as Jorō orb weaver spiders have spread across much of the southeastern United States. Native to eastern Asia, these arachnids feature 1-inch long yellow bodies and 4-inch long yellow-and-black banded legs and weave huge webs that measure several feet in diameter.
These spiders have adapted well to their new environments and may soon expand farther north. If you live in a part of the U.S. where the spiders haven\’t yet arrived, you might be wondering or worrying about them.
How did they get to the U.S. and why are they thriving there? Are they dangerous to humans, pets, and the native environments they\’re entering? Let\’s untangle some of these questions by learning some facts about these fascinating arachnids.
Fact #1: Jorō Spiders Are Less Conniving and Hostile Than Their Namesake
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Known scientifically as Trichonephila Clavata, Jorō spiders get their common name from the Jorōgumo, a type of yōkai or supernatural creature in Japanese folklore. Translated as \”entangling bride\” or \”whore spider,\” the Jorōgumo are cunning, cruel spiders that transform themselves into attractive young women to ensnare young men desperate for love or other favors.
Jorōgumos will lure young men into their homes with promises of love, trap them in extremely strong webs, and use venom to weaken them daily until they die; they savor every moment of their victims\’ demises.
While Jorō spiders in nature will readily eat any mosquitoes, flies, or stink bugs that get caught in their webs measuring 3 to 4 feet in diameter, female spiders are not nearly as hostile towards male spiders or towards humans as the Jorōgumo.
As with other spider species, female Jorōs are significantly larger than male ones, but they don\’t cannibalize their mates after sex like other female spiders often do. Perhaps that\’s why multiple males often feel safe hanging around on a female Jorō\’s web.
Considered possibly the shyest spider species ever, Jorō spiders have been documented to freeze entirely instead of becoming aggressive when disturbed; they wait for the disturbance to stop before they resume moving.
While they are venomous, Jorōs won\’t bite humans or pets unless cornered and their fangs aren\’t large enough to pierce human skin. Researchers observed that Jorō bites only produce localized pain and some slight redness, making them less severe than bee stings.
Fact #2: They Travel Far Through Land and Air
Native to eastern Asian countries like Japan (except for the northern island of Hokkaidō), North and South Korea, Taiwan, and China, Jorō spiders first appeared in the state of Georgia around 2010. It\’s not quite certain how the spiders first arrived in the U.S., but scientists suspect that like many other invasive species, they were unintentional stowaways on an international cargo shipment. In the 14 years since their first arrival,
Jorō spiders have expanded their range from Georgia into North Carolina, South Carolina, Tennessee, Alabama, and parts of Oklahoma, West Virginia, and Maryland.
Jorō spiders are likely to continue moving northward over time. In a study published in Ecology and Evolution in November 2023, researchers at Clemson University in South Carolina concluded that the cooler climates of Great Lakes states like Ohio, New York, and Michigan and the provinces of eastern Canada are more suitable to these spiders than the warmer Southern states they currently occupy.
The spiders might also find Pennsylvania more comfortable since the winter temperatures on the Japanese island of Honshu are roughly equal to those across that state.
Adult Jorōs have been estimated to travel around 10 miles per year, but young spiders can travel faster and further. Shortly after emerging from their egg sacs in the spring, up 400 to 500 young Jorōs can release silk and use it to travel hundreds of miles away via wind currents, a process known as ballooning. Researchers predict that many young Jorōs will balloon into New York and New Jersey some time this summer.
Fact #3: They\’re Invasive But Not Aggressively So…
While researchers have observed that the richness and diversity of native orb weavers are lower in areas where Jorō spiders have moved in, that might not be because Jorōs are driving native species out of their own webs. Rather, Jorōs outbreed other spider species and are willing to spin their webs in areas that native orb weavers typically avoid, such as between powerlines, atop stoplights, and above gas station pumps.
While Jorōs appear to adapt better to noisy, heavily populated human environments, they probably won\’t worry arachnophobes quite as much since they rarely weave their webs inside buildings. Generally, they prefer to spin their webs across open spaces outdoors in the woods or in cities where more insects are likely to fly into their webs and become their meals.
Researchers are still not entirely sure of the extent of the Jorōs\’ impact on the native southern U.S. species. The spiders have become part of the food chain there, taking care of common insect pests and being eaten by birds.
If people are worried about the Jorōs being invasive, they can remove the spiders by hand or with sticks and destroy their egg sacs before the younger ones hatch in the spring, but they shouldn\’t use biocontrol agents or pesticides since those could also harm native spider species.
Final Thoughts
Jorō spiders are likely to stay in the United States for a long time. They\’ve adapted well and continue expanding their territory northward. While they may appear intimidating to some, the spiders seem to pose no major threat to humans, pets, or native spider species as of now.
If you\’re in New York City or Camden this summer and see thousands of tiny spiders gliding down into the streets, you might be more freaked out or repulsed than fascinated. Hopefully, though, learning about the Jorōs have made you a little less anxious about them and a little more interested in how they\’ve made homes in their new environments.
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